The invention relates to a valve for controlling liquids. A valve of this kind has been disclosed by EP 0 477 400. In it, the actuating piston of the valve member is disposed so that it can move in a sealed fashion in a smaller diameter part of a stepped bore, while a larger diameter piston, which is moved by means of the piezoelectric actuator, is disposed in a larger diameter part of the stepped bore. A hydraulic coupling chamber is mounted between the two pistons in such a way that when the larger piston is moved a particular distance by means of the piezoelectric actuator, the actuating piston of the valve member is moved for a distance that is enlarged by the translation ratio of the stepped bore diameter. The valve member, the actuating piston, the larger diameter actuator piston, and the piezoelectric actuator are disposed in series on a common axis.
With valves of this kind, there is the problem of compensating for length changes in the piezoelectric actuator, the valve, or the valve housing by means of the hydraulic coupling chamber. Since the piezoelectric actuator generates a pressure in the coupling chamber to open the valve, this pressure also leads to a loss of coupling chamber fluid. In order to prevent an evacuation of the coupling chamber, a refilling is necessary. A device that is intended to produce this kind of refilling has in fact already been disclosed by the prior art mentioned at the beginning, but this has the disadvantage that a continuous connection that is open in both possible flow directions is provided between the coupling chamber and a reservoir, which significantly influences the operational behavior of the piezoelectric actuator. In particular, a consequently enlarged volume leads to a compressibility that reduces the transmission rigidity of the hydraulic column formed by the coupling chamber.